For many years, computer networks have allowed computing devices to communicate with each other over network links. Despite the growing wireless networking market, many home and corporate networks still rely heavily on physical links, where devices are networked with each other through wires (most commonly, using the Ethernet standard).
When a device is added to a network (and hence, a physical link is established with at least one other device in the network), a number of steps must occur. First, the device must negotiate a physical link with another device in the network. Once that has been established, the devices may then be linked up. Following that, the devices are free to negotiate any parameters they wish regarding layer 2 and higher communications.
At the physical link negotiation stage, IEEE 802.3 provides for a number of physical link parameters that may be negotiated. However, these physical link parameters are limited to those specifically described in the IEEE 802.3 standard. Thus, there is currently no ability to negotiate physical link parameters that were not anticipated by the IEEE 802.3 standard, restricting a company's ability to utilize new physical link parameters in their devices. Furthermore, even for parameters that are described in the IEEE 802.3 standard, there may be times when it is desired to re-negotiate the parameters after the link has been established (e.g., if circumstances change). Current systems lack this ability.
An example of this may be seen in the realm of powering devices using physical links. Savvy businesses have begun to take advantage of the fact that it is possible to transmit power over Ethernet cables. This allows for devices attached to the cables to be powered without the need for batteries or an external plug. For example, an Internet telephone device may be completely powered by the same wire that it uses to transmit and receive voice communications. IEEE 802.3 allows devices to set a “powered” parameter when the link is established, so that the device transmitting the power knows it is safe to do so. However, modern devices may include multiple power settings. For example, if power at the transmitting side is limited, it may be beneficial to have Internet telephones that can operate at less than full power (e.g., eliminating the speakerphone capability on the fly should power availability drop). Such a system, however, is not possible with the current standards for a couple reasons. First, IEEE 802.3 does not provide for the ability to set this type of parameter at the time the link is negotiated. Second, even if it did, there is no mechanism to renegotiate the parameter on the fly while the link is active (e.g., if power availability drops or is diverted to other devices).
Thus, what is needed is a solution that allows for physical link parameters to be negotiated after the physical link has been established. Layer 2 protocol packets could be used for such a feature, but doing so presents a design challenge in networks that may include bridges and repeaters. That is because these devices could potentially lie in between the device transmitting the layer 2 protocol packets and the device ultimately receiving the layer 2 protocol packets, while being transparent to the layer 2 protocol packets. Thus, it is possible that the two endpoint devices may believe they have a direct physical link between them when in reality, a bridge or repeater is between them. Such a condition would throw into doubt any of the layer 2 negotiations that involve physical link parameters. What is needed is a solution that overcomes these drawbacks.